使用PHP中的变量计算函数结果

Question

I have a function that calculates something and want to subtract the result from the variable $bebebe. The result $bebebe only shows the first variable being $testNew. It doesn't show the $testNew-$testest2. Any ideas?

<?php
function testEst() {
    if($_POST["maxkwhresultaat"] > 0){
        echo "" . $_POST['totaal'] . "";
    }
    else
    {
        echo "" . $_POST['maxkwh'] . "</p>";
    }
}
testEst();
?>

<?php
$testest2 = testEst();
$testNew = $_POST["totaal"];
$bebebe = $testNew-$testest2;
?>
    Result: <?php echo $bebebe?>